Replacing a broken window

Either commercial razor knives and you whittle away at it carefully while fitting wedges in it as you go, or braided wire with someone on the inside and someone on the outside pulling the wire back and forth sawing away at it. Both work.

Do you mean the wood on the inside of the cabin and at the top of the window ?.

It the frame and/or trim is wood, you're going to need to razor knife it and put wedges in as you go. Can't use the braided wire without scarring the wood........ But, if you have to ask, it's usually time to call a professional in.

If you are using a razor knife then dish soap is your friend to lubricate the cutting.

Heat gun?

Useless

Wedges and slow steady pressure. I would tap my wood wedges every hour until she began to release. The fish line method can be used to break the seal around the window when your ready for that job. You should pick up a commercial glass suction cup to help handle the window

I ran into that same problem myself. That top wood piece is bedded in really well. Also, the outside handrail screws into it, so make sure you take that off too. I gave up trying to get it off and realized there is only a small 1/2" piece of wood keeping the window from tilting out. You can chisel that off and break the small nails. You also have the break the nails holding the top white track in. Replace the small piece of wood to put it back together. I found you don't really need the nails holding the top track in. Take a look at how I did it here: http://www.yachtforums.com/threads/salon-window-replacement-sliding-to-fixed.24663/#post-215627 One picture shows the small piece of wood coming out. If you don't open that window, you should think about replacing the whole thing and making non-movable. You most likely will have water damage in the lower track. A bigger job than you are planning, but worth it.